Philadelphia was filled with Hollywood transplants on Tuesday evening, as a number of celebrities, such as Meryl Streep and Lena Dunham, took the Democratic National Convention (DNC) stage to speak out in support of Democratic presidential nominee Hillary Clinton.

Meanwhile, that same day, more than 100 high-profile figures in the entertainment industry announced a joint effort to keep Republican nominee Trump out of the White House as part of MoveOn.org's Political Action's #UnitedAgainstHate campaign, writing in an open letter that they "believe it is our responsibility to use our platforms to bring attention to the dangers of a Trump presidency."

As the line between politics and popular culture grows increasingly blurred, an emphasis on celebrity endorsements has become the norm for candidates vying for media attention, especially those belonging to the Democratic Party. But experts say the effectiveness of these endorsements is debatable, as they can be simultaneously beneficial and risky.

The intersection of pop culture and politics is nothing new, says Eric Kasper, an assistant professor of political science at the University of Wisconsin-Eau Claire. Al Jolson sang for Calvin Coolidge, for example, and Frank Sinatra stumped for John F. Kennedy.

"What has changed, though, in our reality TV saturated, 24-hour news cycle, Internet-speed media culture is a greater reliance on celebrities," as well as more outlets for people to find instant fame, resulting in "so many more celebrities now than ever before," says Dr. Kasper in an email to The Christian Science Monitor.

"And given that this election has so far been mostly a personality-driven campaign... celebrities are being deployed by both Donald Trump and Hillary Clinton to bolster their respective levels of popularity, something important for two candidates whom public opinion polls show have historically high unfavorable ratings," he adds.

One benefit of celebrity involvement in politics is increased visibility for both endorser and endorsee, says Darrell M. West, vice president and director of Governance Studies at the Brookings Institution in Washington, D.C..

"Reporters love entertainers who move into politics," he tells the Monitor in an email. "It provides an alternative voice other than conventional politicians and generates a lot of interest among readers and viewers."

When entertainers have their own empire of publicity outlets at their disposal, this partnership can be doubly useful for a candidate: Researchers studying the effect of Oprah Winfrey's endorsement of Barack Obama in 2008 suggest that Ms. Winfrey was responsible for approximately one million additional votes for now-President Obama in the Democratic presidential primary.

But experts say that beyond the financial support and visibility offered by such high-profile figures as Ms. Winfrey, who was able to promote Obama and his stances through her talk show, magazine, and book recommendations, celebrity endorsements typically have very little effect on Americans' voting habits. That is, as one study concluded, people generally aren't more likely to vote for a particular candidate or party just because their favorite actor says they should.

In some cases, celebrity endorsements can even hurt a campaign. Another study found that when people dislike a celebrity and learn that the celebrity has contributed to a political party, they like that party less.

"Celebrity political activity can indeed influence some citizens' views of political parties," writes Anthony J. Nownes, a professor of political science at the University of Tennessee, Knoxville, who conducted the research. With that in mind, using somewhat controversial celebrities such as HBO "Girls" series star Lena Dunham, who spoke on behalf of Hillary Clinton at the DNC on Tuesday, could be considered a risky move.

Even showcasing support from any celebrities at all, regardless of popularity, could be a risk, argues Charlotte Gill in an opinion piece for The Spectator. As evidence, she points to Britain's vote to leave the European Union last month, despite being "bombarded with endorsements for Remain" from a range of celebrities.

American politicians "should take note of the lack of impact celebrities had; it says something," Ms. Gill writes. "Namely that people are resentful toward what they perceive to be a privileged elite. When Clinton poses with Lady Gaga, it may improve her street credibility, but she also runs the risk of alienating massive sections of the voting population."

But Kasper says while politicians are unlikely, for the most part, to attract any significant number of voters, it is nevertheless in the best interest of candidates in close races to take advantage of celebrity endorsements if their opponent is doing the same thing.

In these instances, he compares celebrity support to political yard signs.

"There aren't any people who would be swayed to vote for a candidate based on that candidate's yard signs, but they serve as a signal of the candidate’s level of support," he says. "And if the other side has them, you could look weak if you don't have them too."